In recent years, a fuel cell system has received attention in which a fuel cell to generate a power by an electrochemical reaction of a fuel gas with an oxidizing gas (these gases will hereinafter be referred to as a reactive gas) is used as an energy source. For example, when a solid polymer type fuel cell is disposed in a low-temperature environment at 0° C. or less, proceeding of the electrochemical reaction is disturbed owing to freezing in the fuel cell, especially freezing of a catalyst layer. In such a case, when the fuel cell cannot be restarted after stopping an operation of the fuel cell or even when the fuel cell can be started, a power generation efficiency is remarkably impaired.
For example, in Japanese Patent Application Laid-Open No. 2003-151601, a technology is disclosed in which to stop the fuel cell system, a flow rate of a coolant to the fuel cell is reduced to lower a cooling performance and in which the operation of the fuel cell is continued to raise a temperature of the fuel cell by use of heat generated by the electrochemical reaction. Moreover, in Japanese Patent Application Laid-Open No. 2005-322527, a technology is disclosed in which after the power generation of the fuel cell is stopped and when a temperature difference between a temperature detected by a stack inner temperature sensor and a temperature detected by a stack peripheral temperature sensor exceeds a predetermined value, the coolant is cooled and then introduced into a fuel cell stack.